1. Field of the Invention
The present invention relates to image display apparatuses including supportive structures to resist atmospheric pressure.
2. Description of the Related Art
Nowadays, image display apparatuses utilizing electron-emitting devices, especially, flat displays with a shallow depth, are regarded as replacements for cathode-ray tube displays because of their small sizes and low weights.
Such a flat display apparatus includes a rear plate, a face plate, and frame members that form an airtight case. The rear plate is provided with electron-emitting devices (i.e., a multi-electron-beam source) and the face plate is provided with a light-emitting member (i.e., a phosphor film) that emits light by electron-beam irradiation. The inside of the airtight case is held at a vacuum of about 10−6 Torr. Deformation or breakage of the rear plate and the face plate caused by the differential pressure between the inside and outside of the airtight case tends to occur with an increase in display area of the image display apparatus. Therefore, a means for preventing the deformation and breakage is required. Hence, glass plates (called spacers or ribs) for supporting atmospheric pressure are provided in the airtight case. Consequently, the inside of the airtight case is held at a high vacuum while the distance between the rear plate and the face plate usually ranges from under a millimeter to several millimeters.
It is necessary that the spacers do not significantly affect the electron trajectories between the rear plate and the face plate. However, the spacers affect electric fields near the spacers to bring the electric fields into static changes or dynamic changes caused by charge-up, and these changes in the electric fields lead to changes in electron trajectories. Charge-up of the spacers is assumed to occur because some of the electrons emitted from the electron source or electrons reflected by the face plate enter the spacers and generated secondary electrons are emitted from the spacers; or ions generated by collision of electrons attach to the surfaces of the spacers.
Since positively charged spacers attract electrons traveling near the spacers, displayed images are distorted near the spacers. The effect of charge-up increases with the distance between the rear plate and the face plate.
In order to avoid charge-up, the surfaces of the spacers are generally made conductive. As a result, a small amount of current can flow in the spacers to remove the charge.
Japanese Patent Laid-Open No. 10-302684 discloses such a display apparatus having a structure for improving the electrical connection and the alignment of the spacers and the rear plate; i.e., wiring electrodes on the rear plate are provided with grooves and the spacers abut the grooves.
However, the spacer disclosed in the above-mentioned patent document needs additional improvement in terms of withstand voltage of the spacers.
In the above-mentioned patent document, the grooves are provided in wiring for readily improving the assembly precision. The present invention provides a structure different from such a structure, in order to improve the assembly precision and also improve the withstand voltage of the spacers by a novel technology.